let map = new Map([["name", "yyx"], ["age", 18]])
let set = new Set(["a","b"])
let arr = [1, 2, 3];
let obj = {
  a: 1,
  b: 2,
};
console.log("for...in");
for (let key in arr) {
  console.log(key);
}
console.log("for...in");
for (let key in obj) {
  console.log(key);
}
console.log("for...of");
for (let key of map) {
  console.log(key);
}

for (let key of set) {
  console.log(key);
}